Lymphedema (arm and hand swelling) is a major source of morbidity among breast cancer survivors, yet the basic epidemiology of this problem is poorly understood. This proposal describes an integrated, mentored program of career development and research that will lead to the applicant's development into an independent investigator in population sciences research related to breast cancer. Through an investigation of lymphedema incidence and risk factors in older breast cancer patients, the applicant will gain skills in: 1) the manipulation and analysis of large national administrative datasets; 2) advanced biostatistics related to observational research; and 3) survey methodology. Most studies in the literature addressing lymphedema are cross-sectional and single-institutional with small numbers of patients and the potential for substantial selection bias. A study of a population-based cohort, with prospectively collected data and the power to simultaneously evaluate the relative contribution of multiple potential risk factors, would be a major advance. Utilizing information available from two such databases, we propose three projects. Project 1: Using information provided by an ongoing NCI-funded survey study of older breast cancer patients, for whom Medicare administrative data are also available, we will develop and validate an algorithm using administrative data to identify clinically apparent lymphedema after breast cancer treatment. Project 2: This algorithm will be applied to the NCI's SEER-Medicare linked database of breast cancer patients to determine cumulative incidence curves of lymphedema after breast cancer treatment, and to determine the relative contributions of the initial extent of disease, extent of axillary surgery, initial radiation therapy, and demographic risk factors to the development of lymphedema. Project 3: Using a nested case-control design of the same cohort of patients as studied in Project 1, we will survey these patients for weight-related information to evaluate obesity as a risk factor for lymphedema. The completed algorithm will facilitate subsequent studies of lymphedema in other large administrative databases. The results of this study will also help define priorities for future research addressing such issues as other risk factors, preventive measures, and cost/economic analysis of the burden and treatment of lymphedema.